U.S. patent application number 13/134309 was filed with the patent office on 2011-09-29 for on-press plate development without contamination of fountain fluid.
Invention is credited to Howard A. Fromson, William J. Rozell, William J. Ryan.
Application Number | 20110232517 13/134309 |
Document ID | / |
Family ID | 44654869 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110232517 |
Kind Code |
A1 |
Fromson; Howard A. ; et
al. |
September 29, 2011 |
On-press plate development without contamination of fountain
fluid
Abstract
A method of on-press development of a lithographic printing
plate having an imaged photosensitive (PS) coating by (a) applying
an emulsive film of press ink and fountain onto the entire PS
coating; (b) transferring all nonimage areas of the inked PS
coating and all of the ink film on the nonimage areas of the PS
coating from the plate to a blanket roll while the image areas of
the PS coating remain on the substrate, wherein the nonimage areas
are transferred to the blanket roll in particulate form without
dissolution or dispersion in any ink or fountain; and (c)
contacting the blanket roll with a paper leader to further transfer
all the ink, fountain water, and particles of nonimage PS coating
that were transferred to the blanket roll, from the blanket roll to
the paper leader.
Inventors: |
Fromson; Howard A.;
(Stonington, CT) ; Ryan; William J.; (North
Granby, CT) ; Rozell; William J.; (Simpsonville,
SC) |
Family ID: |
44654869 |
Appl. No.: |
13/134309 |
Filed: |
June 3, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12799568 |
Apr 27, 2010 |
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13134309 |
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12586764 |
Sep 28, 2009 |
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12799568 |
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11493183 |
Jul 26, 2006 |
7816065 |
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12586764 |
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60704140 |
Jul 29, 2005 |
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Current U.S.
Class: |
101/465 |
Current CPC
Class: |
B41C 1/1008 20130101;
B41C 1/1075 20130101; B41C 1/1016 20130101; B41C 2210/24 20130101;
G03F 7/3035 20130101; B41C 2210/08 20130101; B41C 2201/02 20130101;
B41C 2210/04 20130101 |
Class at
Publication: |
101/465 |
International
Class: |
B41N 3/00 20060101
B41N003/00 |
Claims
1. A method of on-press development of a lithographic printing
plate that includes a water-insoluble, oleophilic, radiation-imaged
photosensitive (PS) coating defining image areas and nonimage areas
adhered to a hydrophilic substrate, wherein the method comprises
the sequential steps of: (a) applying a press ink emulsion
containing fountain water in droplets distributed in an ink
continuum as a film onto the entire PS coating to produce an inked
PS coating on the plate; (b) transferring all nonimage areas of the
inked PS coating and all of the ink film on the nonimage areas of
the PS coating from the plate to a blanket roll while the image
areas of the PS coating remain on the substrate, wherein the
nonimage areas of the PS coating are transferred to the blanket
roll in particulate form without dissolution in any fountain water
such that no dissolved PS coating is present in the transferred
fountain water; and (c) contacting the blanket roll with a paper
leader to further transfer all the ink, fountain water, and
particles of nonimage PS coating that were transferred to the
blanket roll, from the blanket roll to the paper leader.
2. The method of claim 1, wherein the imaged plate has (i) a
substrate with a grained and anodized surface, (ii) said PS coating
is a negative working, organic, polymerizable oleophilic coating in
which all active components for polymerization are insoluble in
fountain water or press ink, and (iii) said PS coating is
non-ionically bonded to the substrate and has been imaged by
photo-polymerization, such that the cohesion of the nonimage areas
of the PS coating exceeds the adhesion of the nonimage areas of the
PS coating to the substrate; in said step (b) the ink film adheres
to the blanker roll and is in tension as pulled on between the
blanket roll and the PS coating, thereby (i) transferring only the
nonimage areas of the PS coating from the substrate surface to the
blanket, (ii) in the form of particulate material, and (iii)
without dispersing the nonimage areas of the PS coating into any
fountain water.
3. The method of claim 1, wherein the plate is on a rotating
cylinder of a printing press having an ink roll that applies said
ink film to the PS coating and a rotating blanket roll that is in
contact with the ink film; and said transfer is by the blanket roll
pulling on the ink film and thereby detaching the nonimage PS
coating material adhered to the ink film, off the substrate.
4. The method of claim 1, wherein the nonimage areas have internal
cohesion C1, adhesion to the substrate A1, and adhesion to the ink
A3 and the image areas have internal cohesion C2, adhesion to the
substrate A2, and adhesion to the ink A4; the press ink has
cohesion C3 and adhesion A5 to the blanket roll; and the nonimage
areas of the PS coating have adhesion A6 to the paper leader and
the ink has adhesion A7 to the paper leader; whereby the adhesions
and cohesions are such that the blanket roll pulls the press ink
and the press ink pulls the nonimage areas from the substrate as
undissolved particles that are transferred by the blanket with the
ink to the paper leader.
5. The method of claim 4, wherein the relationship of the adhesions
and cohesions is defined by the following table, in which X/Y is to
be understood as value X> or < value Y and the Ai and Ci row
and column headings are the adhesions and cohesions as described
with respect to FIGS. 8-10: TABLE-US-00013 X/Y C1 C2 C3 A1 A2 A3 A4
A5 A6 A7 C1 -- < N/A > < < N/A < N/A N/A C2 > --
> > < > > > N/A N/A C3 N/A < -- > < >
< < N/A N/A A1 < < < -- < < N/A < N/A N/A
A2 > > > > -- N/A > N/A N/A N/A A3 > < <
> N/A -- N/A < N/A N/A A4 N/A < > N/A < N/A -- <
N/A N/A A5 > < > > N/A > > -- < < A6 N/A
N/A N/A N/A N/A N/A N/A > -- N/A A7 N/A N/A N/A N/A N/A N/A N/A
> N/A --
6. The method of claim 2, wherein the plate is on a rotating
cylinder of a printing press having an ink roll that applies said
ink film to the coating and a rotating blanket roll that is in
contact with the ink film; and said transfer is by the blanket roll
pulling on the ink film and thereby detaching nonimage PS coating
material adhered to the ink film, off the substrate.
7. The method of claim 6, wherein the nonimage areas have internal
cohesion C1, adhesion to the substrate A1, and adhesion to the
applied ink A3 and the image areas have internal cohesion C2,
adhesion to the substrate A2, and adhesion to the applied ink A4;
the ink has cohesion C3 and adhesion A5 to the blanket roll; and
the nonimage areas of the PS coating have adhesion A6 to the paper
leader and the ink has adhesion A7 to the paper leader; whereby the
adhesions and cohesions are such that the blanket roll pulls the
ink and the ink pulls the nonimage areas from the substrate as
undissolved particles that are transferred by the blanket with the
ink to the paper leader.
8. The method of claim 7, wherein the relationship of the adhesions
and cohesions is defined by the following table, in which X/Y is to
be understood as value X> or < value Y and the Ai and Ci row
and column headings are the adhesions and cohesions as described
with respect to FIGS. 8-10: TABLE-US-00014 X/Y C1 C2 C3 A1 A2 A3 A4
A5 A6 A7 C1 -- < N/A > < < N/A < N/A N/A C2 > --
> > < > > > N/A N/A C3 N/A < -- > < >
< < N/A N/A A1 < < < -- < < N/A < N/A N/A
A2 > > > > -- N/A > N/A N/A N/A A3 > < <
> N/A -- N/A < N/A N/A A4 N/A < > N/A < N/A -- <
N/A N/A A5 > < > > N/A > > -- < < A6 N/A
N/A N/A N/A N/A N/A N/A > -- N/A A7 N/A N/A N/A N/A N/A N/A N/A
> N/A --
9. The method of claim 1, wherein all the active ingredients in the
nonimage PS coating are transferred by the blanket to the paper in
particles adhered to press ink, without dissolution or dispersion
of the active ingredients in any fountain water or press ink.
10. The method of claim 9, wherein none of the ingredients of the
PS coating are soluble or dispersible in water or ink; the PS
coating contains a water-insoluble colorant; and all the
ingredients in the nonimage PS coating are transferred by the
blanket to the paper in particles adhered to press ink, without
dissolution or dispersion in any fountain water or press ink.
11. The method of claim 5, wherein none of the ingredients of the
PS coating are soluble or dispersible in water or ink; the PS
coating contains a water-insoluble colorant; and all the
ingredients in the nonimage PS coating are transferred by the
blanket to the paper in particles adhered to press ink, without
dissolution or dispersion in any fountain water or press ink.
12. A method of developing a lithographic plate having a
hydrophilic substrate covered by an imaged photosensitive (PS)
coating wherein the PS coating contains water-insoluble active
ingredients including a polymer, a monomer and/or oligomer, at
least one polymerization or cross link initiator, and a dye
compound, in a printing press where the imaged plate is mounted on
a plate cylinder, a press ink film emulsion of fountain water
droplets entrained in a continuous medium of ink is applied on the
PS coating by an ink form roll in contact with the coating when the
plate is on the plate cylinder, followed by a blanket roll
contacting the PS coating when the plate is on the plate cylinder
and a rubber roll opposed to the blanket roll, with a paper leader
running between the blanket roll and the rubber roll, comprising
the steps of: (a) rotating the rolls multiple revolutions whereby
with each revolution increasing areas of the plate substrate are
revealed as successive particles of nonimage PS coating are
randomly removed from the plate substrate by the blanket roll
applying sufficient tension to the ink emulsion whereby the ink
emulsion pulls only nonimage areas from the substrate in the form
of undissolved PS coating particles including said initiator and
dye compound that are transferred by the blanket with the ink
emulsion to the paper leader; (b) splitting the ink emulsion,
whereby (i) the ink emulsion film on the imaged areas splits such
that a separation portion adheres to the blanket while a retained
portion remains adhered to imaged areas and (ii) some of the
entrained water in the emulsion separates from the emulsion and
deposits on the revealed substrate and some of the entrained water
remains in the emulsion that pulls off the nonimage areas; (c)
whereby when all of the nonimage PS coating has been removed from
the substrate by transfer to the blanket roll, the plate has been
developed with none of the active ingredients of the PS coating
present in the water that separated from the emulsion and was
deposited on the substrate.
13. The method of claim 12, wherein all the active ingredients in
the nonimage PS coating are transferred by the blanket to the paper
as particles adhered to press ink, without dissolution of the
active ingredients in the water remaining in the emulsion that
pulled off the nonimage areas.
14. The method of claim 13, wherein none of the active ingredients
are soluble or dispersible in ink or water; and all the active
ingredients in the nonimage PS coating are transferred by the
blanket to the paper in particles adhered to the ink emulsion that
pulls off the nonimage areas, without dissolution or dispersion of
the active ingredients in any press ink.
15. The method of claim 12, wherein the coating contains a
water-insoluble colorant; when all of the nonimage PS coating has
been removed from the substrate by transfer to the blanket roll,
the plate has been developed with none of the active ingredients or
colorant of the PS coating present in the fountain water that
separated from the emulsion and was deposited on the substrate; and
all the active ingredients and colorant in the nonimage PS coating
are transferred by the blanket to the paper in particles adhered to
press ink, without dissolution of the active ingredients in the
water remaining in the emulsion that pulled off the nonimage
areas.
16. The method of claim 15, wherein none of the active ingredients
are soluble or dispersible in ink or water; and all the active
ingredients in the nonimage PS coating are transferred by the
blanket to the paper in particles adhered to the ink emulsion that
pulled off the nonimage areas, without dissolution or dispersion of
the active ingredients in any press ink.
17. The method of claim 16, wherein none of the ingredients of the
PS coating are soluble or dispersible in water or ink.
18. A method of on-press development of a printing plate having a
photosensitive (PS) coating with a pattern of image and nonimage
areas on a substrate, in a lithographic printing press including a
plate cylinder on which the plate is mounted for continuous
rotation, an ink form roll for continuously applying a press ink
film emulsion including fountain fluid on the coating as the plate
rotates, a blanket roll engageable with the plate downstream of the
ink form roll, and print media engageable with the blanket, whereby
ink is transferred from the plate to the blanket and further
transferred from the blanket to the print media, said method
comprising: with the blanket and a film of press ink between the
blanket and the PS coating on the plate, mechanically dislodging
and removing all the nonimage PS coating areas of the plate from
the substrate as particles; with the blanket, transferring all the
removed PS coating particles onto the print media; whereby none of
the nonimage PS coating dissolves or disperses in the ink
emulsion.
19. The method of claim 18, wherein all the active ingredients in
the nonimage PS coating are transferred by the blanket to the print
media in particles adhered to press ink, without dissolution or
dispersion of the active ingredients in any fountain water or press
ink.
20. The method of claim 18, wherein none of the ingredients of the
PS coating are soluble or dispersible in water or ink; the PS
coating contains a water-insoluble colorant; and all the
ingredients in the nonimage PS coating are transferred by the
blanket to the paper in particles adhered to press ink, without
dissolution or dispersion in any fountain water or press ink.
Description
RELATED APPLICATIONS
[0001] This is a continuation-in-part of U.S. application Ser. No.
12/799,568 filed Apr. 27, 2010 for "Processless Development of
Printing Plate", which is a continuation-in-part of U.S.
application Ser. No. 12/586,764 filed Sep. 28, 2009 for
"Non-Chemical Development of Printing Plates", which is a
continuation-in-part of U.S. application Ser. No. 11/493,183 filed
Jul. 26, 2006 for "Imageable Printing Plate for On-Press
Development", which claims priority under 35 U.S.C. .sctn.119(e)
from U.S. Provisional Application No. 60/704,140 filed Jul. 29,
2005, for "Imageable Printing Plate for On-Press Development", and
benefit under 35 U.S.C. .sctn.120 is also claimed from U.S.
application Ser. No. 11/821,721 filed Jun. 25, 2007 for "Water
Spray Development of Planographic Plates" and U.S. application Ser.
No. 12/215,124 filed Jun. 25, 2008 for "Heated Water Spray
Processor". The complete disclosures of these applications are
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to the on-press processing of
imaged lithographic printing plates.
[0003] Plates of interest have a solvent-soluble,
radiation-polymerizable, oleophilic resin coating on a hydrophilic
substrate. In conventional practice, after image-wise exposure at
ultraviolet (UV), visible, or infrared (IR) wavelengths, the plates
are developed with solvent to remove the unexposed areas of the
coating by dissolution, thereby producing a substantially
planographic pattern of oleophilic and hydrophilic areas. The
developed plates are then ready for mounting on a cylinder of a
printing press, where the plates are subjected to fountain fluid
and ink for transfer of ink to a target surface according to the
pattern of oleophilic and hydrophilic areas on the plate.
[0004] Although a process is known for developing IR imaged plates
with water rather than solvent, the coating is not polymerized by
the imaging. Instead, the coating contains microspheres or beads of
thermally fusible material suspended in a water-soluble medium or
matrix. The plate is imaged at high energy levels (250-350
mj/cm.sup.2) such that the microspheres fuse to themselves and the
substrate. The imaged plates can be developed with water or
fountain fluid on-press, whereby the imaged, fused areas remains
intact whereas the unimaged, non-fused areas including microspheres
are removed via dissolution of the matrix.
[0005] Not only is a high level of energy required for imaging such
plates, but the rate of imaging is slow and the resolution is low.
Also, the dissolved matrix with microspheres is a chemical waste
that must be specially treated.
[0006] Thus, it should be appreciated that almost all existing
negative-working planographic lithographic printing plates, with
the exception of those produced by ablation in the imager, are
produced by laying down a continuous film of radiation-sensitive
coating on a suitable hydrophilic substrate such as grained,
anodized, and hydrophilized aluminum sheet, or its equivalent,
imaging the radiation-sensitive coating with actinic ultra-violet,
violet, or infra-red energy in an image-wise fashion, and
subsequently subtracting the non-irradiated portions of the imaged
plate by the process of solubilization or dispersion, thus
establishing oleophilic image areas and water receptive non-image
areas.
[0007] The water soluble materials that are used in these coatings
typically comprise polymers, monomers, and various components of
the initiator system and in some cases additives. The purpose of
using these water soluble materials is to aid in the development
that takes place on press. These materials are needed to insure
that the non imaged areas of the plate are completely "cleaned out"
and remain water receptive. The main problem with this type of
development is that these water soluble materials dissolve in the
fountain solution.
[0008] Dissolution of these water soluble materials results in two
very distinct problems. First, the colorant system that is used in
the coating (usually a blue green material) mixes with the colored
inks, causing them to shift in color. Second, the water soluble
materials also act as emulsifiers which cause the ink to emulsify
in the fountain solution. As a consequence, the ink and water can
no longer differentiate between imaged and background areas. This
causes the plate to scum in the background and image to go
blind.
SUMMARY
[0009] A photosensitive (PS), especially IR sensitive, coating is
comprised of water insoluble active materials. When the coated
plates are developed on press the PS coating is removed from the
background (non image) areas of the plate in a totally solid phase.
There is no resin, dye, or colorant in the PS coating that will
dissolve or disperse in either the fountain solution or the press
ink.
[0010] Such PS coating that is removed from the plate is also
completely removed from the press by being carried out with the
printed waste or leader paper during the initial roll up. This is
in contrast with known press-developable coatings in which water
soluble raw materials are incorporated into the coating. Use of non
water soluble materials eliminates these problems completely.
[0011] According to one aspect, the method relies on the blanket
and a film of press ink between the blanket and the PS coating on
the plate, to mechanically dislodge and removing all the nonimage
PS coating areas of the plate from the substrate as particles. The
blanket then transfers all the removed PS coating particles onto
the print media, whereby none of the nonimage PS coating dissolves
or disperses in the ink emulsion.
[0012] The fracturing phenomenon and removal of the unimaged film
in particulate form only, is attributable to the combined factors
that the as-dried PS coating on the plate is not soluble in water
and has an adhesion to the plate substrate that is less than its
cohesion. By subjecting the entire imaged surface to this
mechanical force the unimaged areas of the PS coating are
mechanically dislodged from the substrate in the form of
particulate matter in solidus, i.e., without any solubilization or
dispersion process.
[0013] Furthermore, because the fractured particles have not
undergone solubilization, they do not adhere to each other to form
agglomerates in the processor, nor do they adhere to the rubber,
polymer, or metal of the processor or the plate.
[0014] On-press the high-tack press inks adhere very well to the
imaged plate surfaces, in both the imaged and unimaged areas.
During start-up, when the blanket compresses against the inked
surface of the imaged plate, the high-tack adhesion of the ink to
the blanket exceeds the adhesion of the unimaged areas of the
plate, and the cohesion of the unimaged areas of the plate also
exceeds the adhesion to the plate, so the fractured non-image
particles are pulled onto the blanket and deposited on the paper
web by the blanket and eventually end up in the initial start-up
paper waste. The imaged areas have both adhesion and cohesion
greater than the ink.
[0015] It should be appreciated that, whereas the active
ingredients in the dried, unimaged areas of the PS coating are only
soluble in a non-aqueous solvent, these areas are removed (i.e.,
the plate is "developed") without use of any such solvent. In this
context, "active" means an ingredient that participates in the
radiation induced polymerization in the imaged areas. This
generally means the active ingredients are a polymer, a monomer
and/or oligomer, at least one polymerization or cross link
initiator, and a dye.
[0016] The imageable PS coating as initially applied and dried on
the substrate, has a relatively low degree of adhesion to the
substrate. This is preferably achieved by using a substrate having
a grained, positively charged (anionic) hydrophilic surface to
which the coating mildly adheres non-ionically as a result of
drying. Such substrate can be a grained aluminum sheet treated with
silicate or other known hydrophilizing agents. Drying produces a
mild degree of cohesion, such that the bottom surface of the
coating mechanically interengages and thus adheres to the
irregularities in the grained surface of the substrate, and the
body of the coating achieves sufficient cohesion to permit further
handling, shipment, and imaging of the plates. For on-press
development, the cohesion of the dried, unimaged coating is greater
than its adhesion to the substrate and its tack or adhesion to the
ink and blanket roll is greater than its adhesion to the substrate,
but the adhesion of the imaged coating to the substrate is greater
than its adhesion to the ink.
[0017] Upon imaging of the plates, the radiation induced
polymerization causes the adhesion and cohesion of the imaged areas
to become much higher than the adhesion and cohesion of the
unimaged areas. Diazo compounds have been used by some
practitioners to increase the adhesion of imaged areas in
essentially photopolymerizable coatings. However, the coatings for
use in the present invention are diazo-free, because with diazo
based coatings (whether applied in aqueous or non-aqueous solution)
the dry coating bonds ionically to the substrate and can only be
removed via chemical reaction with non-aqueous (organic)
solvent.
[0018] Without limiting the scope of the claims corresponding to
the inventive concept, we can ascribe the best results at least in
part to a combination of non-diazo based resins and associated
polymerization initiating agents, which produce low adhesion to the
substrate in the manufactured plate yet can quickly produce high
adhesion where radiation imaged.
[0019] Practitioners in this field had no reason to investigate or
optimize the difference in adhesion of non-aqueous
photopolymerizable resins as a basis for non-chemical, and
especially mechanical, removal of the nonimage areas. Because it
was the established practice that nonimage areas of the imaged
plate could be substantially completely dissolved by the non
aqueous developer solution, the main objective of others for
improving coatings has been to increase the adhesion, cohesion, and
durability of the imaged areas and thereby enable the plate to
better withstand the rigors of the printing press. Any desired
relationship between the imaged and unimaged areas was based on
relative solubility, not relative mechanical adhesion, to minimize
incidental dissolution of any of the exposed surface of the imaged
areas while the developer solution dissolved substantially all of
the non image areas. The present invention avoids such incidental
dissolution of the imaged areas because the development mechanism
does not rely on dissolution or dispersion.
[0020] The plates can be heated after imaging to increase the
difference in cohesion and adhesion of the coating to the substrate
as between the imaged and unimaged areas, such that a greater force
can be applied to the plates to dislodge only the unimaged areas.
In particular, a thermally imageable negative working plate can be
exposed to heat for a short period of time after imaging, whereby
the imaged portions become more stable and tougher, while the
portions of the coating that are to be removed are not
significantly affected. The heating step preferably, but not
necessarily, immediately follows the imaging step, but can be at a
different location from the imaging step.
[0021] In a further preference, the water soluble top coat
conventionally used to protect photosensitive (PS) coatings is
washed off the PS coating after imaging (and after any subsequent
heating step) and the plates stored temporarily until mounted on
press. The top coat is typically a water soluble film former (such
as PVOH) that prevents atmospheric oxygen from diffusing into the
coating and quenching the free radicals necessary for inducing
polymerization. The removal of this topcoat has been found to
substantially immunize the imaged coating from further
polymerization in the unimaged areas due to ambient light. Thus,
the plates need not be handled in yellow or other special light
between imaging and mounting on press.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 schematically shows a printing system comprising
plate stack, imager, and press;
[0023] FIG. 2 is a schematic plate cross section showing an
imageable coating directly supported on a substrate;
[0024] FIG. 3 is a schematic plate cross section showing an
imageable plate with a subcoat and top coat;
[0025] FIG. 4 is a schematic plate cross section upon exposure to
radiation;
[0026] FIG. 5 is a schematic of on-press development of an imaged
plate;
[0027] FIG. 6 is a schematic plate cross section showing the
pattern of remaining oleophilic imaged areas of the coating and the
hydrophilic substrate surface areas where the unimaged areas have
been removed in solidus;
[0028] FIG. 7 is a schematic of one embodiment of a pre-press water
processor;
[0029] FIG. 8 is a schematic representation of the interface
between the imaged plate and the blanket roll during development
on-press;
[0030] FIG. 9 is a schematic representation of the interface
between the imaged plate and the blanket roll as the roll pulls off
the unimaged areas during development on-press;
[0031] FIG. 10 is a schematic representation of the interface
between the blanket roll and the printable media as the ink and
unimaged material is transferred to a waste leader during
development on-press; and
[0032] FIG. 11 is a matrix showing the relationships of the
adhesion and cohesion among the unimaged coating, imaged coating,
substrate, ink, ink roll, blanket roll, and printable media during
the on press development represented in FIGS. 8-10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Printing Press Process
[0033] FIG. 1 shows a schematic of a printing plant 10, such as for
newspaper printing, in which a stack of radiation imageable plates
12 is situated upstream of an imager 14, where the coating on the
plates is selectively highly cross linked by selective exposure to
radiation to form a pattern of highly cohesive and adhesive areas,
and areas that exhibit less cohesion and adhesion. The plate
substrate is hydrophilic, whereas the coating is oleophilic. The
radiation exposure produces high internal cohesion, and high
adhesion to the plate. In a conventional negative working system,
the original (unimaged) coating is soluble in a specified developer
solvent, so the imaged plate must be developed with such solvent to
remove the non-exposed areas and thus produce a plate usable in the
press. The developer solutions most frequently used contain either
some amount of an organic solvent (typically benzyl alcohol) or
have an elevated pH (alkaline).
[0034] Unlike conventional systems, the present invention delivers
the imaged plates directly from the imager 14 to the press 16,
wherein contact with the ink form roll 20 and blanket roll (not
shown) remove the non-image areas. In another embodiment fountain
fluid 18 may also be employed 20. The unimaged coating material is
quickly dislodged to reveal areas of the underlying substrate,
which have an affinity for fountain fluid, and the retained imaged
areas, which have an affinity for ink. Once developed in this
manner, the resulting printing plates can be run in the
conventional fashion to produce the printed product, which is
output at 22.
[0035] As an optional configuration, the imaged plates may be sent
to a processing station 24, where no special treatment is required
other than contact with a spray of pH neutral water (e.g., tap
water). A preferred spray can be achieved with a nozzle pressure
over about 1000 psi, but if accompanied by brushing or similar
wiping action the water pressure can be lower. This wiping can be
achieved as part of or immediately after the water processing at
24. The plates can then be dried and stacked, before a fully or
substantially fully processed plate is sent to the press 16.
[0036] The most evident advantages of the foregoing process, are
that no separate developing equipment or step is required between
the imager 14 and the press 16, and no resin is dissolved or
dispersed into the process water. Rather, all or most of this
coating detaches from the substrate in sufficiently large pieces
that can be readily removed by filtration and relatively easily
disposed of.
Imageable Plate
[0037] FIGS. 2-6 illustrate schematically, the physical attributes
of a plate according to the present invention. FIG. 2 is a
schematic section view of the basic embodiment 26, consisting of a
substrate or carrier S on which an organic, non-aqueous
solvent-based coating C has been applied and dried. The substrate S
is preferably a grained, anodized aluminum sheet. The substrate is
preferably post treated with a hydrophilizing agent prior to
coating. Such post treatments are well known in the art, and
include silicate solutions, polyvinylphosphonic acid (PVPA) or
amino trimethylenephosphonic acid (ATMPA). The coating C is applied
from a solvent soluble composition comprising one or more
components capable of cross linking by free radical polymerization.
The polymerization arises as a result of imaging with ultraviolet,
visible or infrared radiation. As such, the coating may further
comprise radiation absorbers and/or initiators to facilitate the
cross linking efficiency. None of these active components is
soluble in water. Preferred coating compositions further comprise a
polymeric material to enhance the oleophilicity and durability of
the coating in the ink receptive printing areas.
[0038] FIG. 3 is a schematic section view of a plate according to
an alternative embodiment where a subcoat SC has been applied to
the substrate S, the imageable coating C is applied over the
subcoat, and a topcoat TC is applied over the imageable coating.
The top coat TC is typically a water soluble film forming layer
such as polyvinyl alcohol (PVOH) that serves to prevent atmospheric
oxygen from diffusing into the coating and quenching the free
radicals. Without the topcoat, the polymerization efficiency is
dramatically decreased. The subcoat SC is a water soluble material
that facilitates the release of the coating from the substrate in
the unimaged areas. The subcoat SC must not adversely impact the
adhesion of the coating to the substrate in the imaged areas of the
coating. 4-hydroxybenzene sulfonic acid, sodium salt has been found
to be particularly suitable as a subcoat.
[0039] FIG. 4 corresponds to FIG. 2, and illustrates the effect on
the coating of exposure to imaging radiation. The radiation source
is preferably a digitally controlled laser, which produces exposure
pixels such that a pattern of unexposed coating 38a, 30b, and 30c
and exposed coating 32a and 32b covers substantially all of the
plate. However, any of the sources of incident imaging radiation
used in the art to form selectively written surfaces can be used.
The selective imaging results in relatively distinct boundaries 34
at the interface between the imaged and unimaged areas. It should
be appreciated that the Figures are not to scale, especially as to
relative thickness of the coating and substrate, but are merely
illustrative. For the illustrated negative working plate, the
exposed coating in areas 32a, 32b becomes highly cross linked,
thereby creating areas that have sufficient cohesion and adhesion
such that they are not removable by subjecting these areas to
substantial mechanical forces or pressure. The unexposed areas 30a,
30b, and 30c retain the original characteristics and properties of
the dried coating before imaging. This material is not highly cross
linked, and lacks the adhesion to withstand substantial mechanical
forces or pressure.
[0040] FIG. 5 illustrates the context of development on press 100.
The imaged plate 102 has been mounted to a plate cylinder 104 in
contact opposition to an ink form roll 106 and a blanket roll 108.
The ink roll is generally made of rubber and the ink is generally
supplied to the ink roll from a source 110 as an emulsion of water
in a continuous ink medium. A fountain fluid distributor 112 is
provided for the plate cylinder 104 and a rubber roll 114 is in
opposition to the blanket roll 108.
[0041] During normal printing with a developed printing plate,
press ink is applied to the rotating plate 102 and it immediately
splits, with the ink portion attracted to the oleophilic areas and
the water portion attracted to the hydrophilic areas. Fountain
fluid is deposited on the upper portion of the plate 102, to
further assure that the ink portion and water find the oleophilic
and hydrophilic areas, respectively, thereby defining the image
pattern of ink to be printed on the target medium (e.g., paper).
This pattern of ink is first transferred to the blanket 108, which
transfers the ink to the paper 116 as the paper passes between the
blanket 108 and the opposed rubber roll 114.
[0042] With the present invention, after a new plate 102 is mounted
on the plate cylinder 104, the plate cylinder is rotated and the
ink form roll 106 is activated, with or without activation of the
fountain fluid supply 112, depending on whether the plate has a
water soluble top coat. A film of press ink emulsion arises between
the ink roll cylinder 106 and the entire surface of the plate 102.
The continuous press ink medium adheres to the entire (oleophilic)
surface of the plate, exhibiting sufficient cohesion and adhesion
to detach the ink from the ink roll 106. However, the adhesion of
the unimaged areas of the plate 102 to the substrate is so low that
the blanket 108 pulls the unimaged areas off the substrate, as
frangible particles. Thus, the mechanical removal forces are
applied by the blanket roll pulling ink and unimaged coating
material adhered to the ink, off the substrate. For this to occur,
in the unimaged areas the adhesion (tack) and cohesion of the ink
exceed both the cohesion of the coating and its adhesion to the
substrate, and the adhesion of the ink to the blanket exceeds the
adhesion of the unimaged areas to the substrate. These particles
are transferred by the blanket roll 108 to the paper 116. As with
conventional startup of a newly installed plate, a paper leader or
sacrificial paper sheets are passed through the press during up to
a few hundred startup revolutions of the plate roll 104. With the
present invention, these startup revolutions completely remove the
non-image areas, with all of the removed coating material
transferred to the sacrificial sheets 116. These can be disposed of
as solid waste, without chemical treatment. After startup, the
fountain supply 112 is activated and normal printing begins on the
developed plate.
[0043] FIG. 6 shows a portion the resulting plate 26 (flattened for
convenience) ready for production runs with areas 32a and 32b
representing the oleophilic coating areas that pick up ink and 42a,
42b, and 42c representing the hydrophilic substrate surfaces that
carry the fountain fluid. It is to be understood that the plates
and process described herein are essentially planographic and, as
noted above, the relative thickness of the areas and surfaces shown
in the figures should not be considered as in scale.
[0044] FIG. 7 is a schematic of the operative components of one
possible processor 200 for the optional pre-press water development
of an imaged plate in a system as depicted in FIG. 1 (where the
water processor is indicated at 24). It should be appreciated that
the coating formulation and its relationship to the substrate and
press ink, offers the options of development with rotating brushes
in an aqueous environment, development on press in reliance on the
tack of the ink and blanket roll, or a combination of the two. In
the illustrated development, the imaged plate 202 is conveyed over
a basin or tank 204 onto a platen 206 or the like. In one option a
high pressure spray 208 impinges on the plate surface and
mechanically removes the unimaged areas from the substrate, as
particles, but a more cost-effective option is for simple water
deposition with reliance on the mechanical action of a rotary the
brush 210 to achieve the removal. The overflowing water with
removed particles is captured in the basin or sump 204 and
continuously drained and delivered via line 212 to particle filter
214. The filtered water is recirculated back to the spray nozzle
218 by pump 216 and return line 218. The resinous material removed
as particles is trapped in the filter, so there is little or no
chemical treatment required of the waste stream associated with
developing the plate.
[0045] One significant advantage is that the unimaged areas of the
plate have less tendency to retain ink receptive coating residue
than on a conventionally developed plate. With conventional
development, the coating must be completely dissolved and removed
in the developing step. It is sometimes problematic to ensure that
all coating is removed from the interstices of the substrate grain.
Any residual will remain during the printing process and cause some
level of ink pick-up in the background. With the present invention,
the coating in the background areas is only mildly adhered to the
substrate, so is fully removable. In any event, even a residual of
coating material will be removed soon after printing start-up,
resulting in a cleaner background.
[0046] Another significant advantage is that the integrity of the
imaged coating is not adversely affected by the processing liquid,
i.e., water or fountain fluid. For conventional plates, the imaging
process causes a change in the solubility of the coating in the
developer. The change is never 100% efficient; that is, even the
imaged coating will have some level of solubility in the developer.
This residual solubility may significantly alter the adhesive
and/or cohesive integrity of the coating. The present invention
does not suffer from this problem.
Coating of Representative Embodiment
[0047] In one embodiment associated with the basic configuration
shown in FIG. 2, the coating comprises from about 5 to about 30 wt
% based on solids content, of a polymer that is generally
considered by practitioners of applied chemistry, as insoluble in
water. The polymer material may be selected from a wide range of
types such as but not limited to acrylates, siloxanes, and styrene
maleic anhydrides.
[0048] Advantageously, the coating comprises from about 35 to about
75 wt % based on solids content, of a polymerizable monomer, a
polymerizable oligomer, or combination thereof that is similarly
insoluble in water. Some suitable radically polymerizable (cross
linkable) materials are a multifunctional acrylate such as Sartomer
399 and Sartomer 295 commercially available from Sartomer Co.
[0049] The coating comprises a non-water-soluble initiator system
capable of initiating a polymerization reaction upon exposure to
imaging radiation. Some suitable initiator systems comprise a free
radical generator such as a triazine or an onium salt.
[0050] Additional optional components include dyes that absorb the
imaging radiation (e.g. infrared absorbing dyes) and pigments or
dyes that serve as colorants in the coating.
[0051] The coating can include a "release agent" such as
4-hydroxybenzene sulfonic acid, sodium salt 4-HBSA,
4-hydroxybenzoic acid or sodium benzoate. In a different embodiment
the release agent is disposed as a sub-coating between the
hydrophilic substrate and the imageable coating.
EXAMPLES
[0052] In a first trial at a commercial newspaper printing
facility, a negative working, photopolymerizable plate was imaged
with IR radiation at 90 mj/cm.sup.2 and developed on press during
startup as described above, then used in the normal manner to print
over 100,000 high quality newspaper sheets. The plate was
constituted as follows:
[0053] (a) grained, hydrophilized aluminum substrate
[0054] (b) imageable coating comprising the raw materials [0055]
(i) organic solvent [0056] (ii) polyvinyl butyral polymer resin
[0057] (iii) penta functional acrylate monomer [0058] (iv) pigment
dispersion [0059] (v) stabilizer [0060] (vi) IR dye [0061] (vii)
organo-borate catalyst [0062] (vii) onium salt catalyst [0063]
(viii) partially water soluble additive (DTTDA)
[0064] (c) PVOH topcoat
[0065] After thermal imaging, the plate was post-heated. It is
believed this step produces further cross linking in the imaged
areas but not in the unimaged areas. After cooling, the topcoat was
washed off with tap water. Several hours after the topcoat was
removed, the plate was mounted on the plate cylinder of a
commercial newspaper printing press, with standard news paper, ink
roll, blanket roll and rubber roll set up. During startup only the
ink roll was active, and the plate was developed and background
areas satisfactorily cleaned out within about 300 revolutions of
the plate cylinder.
[0066] Another trial press run was made with a plate that was
identical to that of the first run, except for the omission of the
partially water soluble organic compound (DTTDA) stabilizer. The
results showed no significant difference. For commercial
production, another, water-insoluble stabilizer (e.g., for
increasing shelf-life) can be used if necessary.
[0067] These trials support the conclusion that unimaged areas can
be cleaned out on press corresponding to print dot (pixel) density
targets between 0 percent to at least about 98 percent, and most
likely at least 99 percent.
[0068] If the plates are developed off-press with water and
brushing or other devise that impinges or impacts, the targets are
achieved between about 0 percent to about 97 percent. The remaining
unimaged coating is not a thin layer, but rather in the form of
small clumps that cling to the substrate at the corners of certain
imaged letters, numbers, and symbols. This remaining material is
cleaned out with the ink roll onto the blanket and paper on
press.
[0069] FIGS. 8-11 disclose in greater detail the manner in which
the unimaged coating is removed from the substrate (i.e., the plate
is "developed") on press. FIG. 8 is a schematic representation of
the interface between the imaged plate and the blanket roll during
development; FIG. 9 is a schematic representation of the interface
between the imaged plate and the separating blanket roll during
development; FIG. 10 is a schematic representation of the transfer
of ink and unimaged coating from the blanket roll to the printable
media; and FIG. 11 is a matrix showing the relationships of the
adhesion and cohesion among the unimaged coating, imaged coating,
substrate, ink, ink roll, blanket roll, and printable media during
the on press development represented in FIGS. 8-10. In these
Figures, arrows with alphanumeric identifiers point to either the
inside of a given material (to indicate cohesion) or to the
interface between two materials (to indicate adhesion). "A"
indicates adhesion and "C" indicates cohesion.
[0070] FIG. 11 shows the desired relationships among the adhesions
and cohesions, to be understood by first selecting an A or C entry
in the first column and then finding its relationship to another A
or C at the intersection of the row of the first selection and the
column of the other A or C. For example, C1 is greater than A1 and
C1 is less than A3 (which is equivalent to A1 less than C1 and A3
greater than C1).
[0071] FIG. 8 shows the condition on press, after the ink has been
applied to the imaged plate and the inked plate has been rotated
into contact with the blanket. Whether pure ink or an emulsion of
water in pure ink was applied (collectively, "ink"), the ink
adheres to the entire coating, because at this point the entire
coating is oleophilic.
[0072] FIG. 9 shows a subsequent point in time, at which the imaged
plate on the plate cylinder is separating from contact with the
blanket. In the unimaged regions the tack and cohesion of the ink
exceeds the adhesion of the coating to the substrate, and the
cohesion of the coating exceeds its adhesion to the substrate. The
split in the unimaged regions occurs between the coating and the
substrate. The unimaged regions are removed in solidus from the
substrate along with the overlying ink, while attached to the
surface of the ink and without dispersing into the ink. No
dissolution of the coating should occur or the split would take
place within the coating and leave some coating on the substrate.
In the imaged regions, the adhesion of the coating to the substrate
and its cohesion exceed the cohesion of the ink, thus causing the
ink to split within itself, such that some ink remains on the
imaged regions of the coating and some remains on the blanket.
[0073] FIG. 10 depicts the interaction of the blanket after
separation from the plate, with the sacrificial paper or leader on
which the removed coating material is transferred for disposal. The
ink and attached particles of unimaged coating preferentially
adhere to the paper, which goes to waste disposal. The area of the
blanket where such transfer occurred is returned into contact with
the plate as depicted in FIG. 8. This is repeated until all the
unimaged coating has been removed from the entire plate, thus
"developing" the plate. The developed plate has a pattern of areas
of hardened, oleophilic coating material and hydrophilic substrate,
which are compatible with conventional wet lithographic printing
presses.
[0074] It should be appreciated that whether development is fully
or partially implemented pre-press or on-press, the coating is not
dispersible in water (or equivalent fountain solution) or ink,
i.e., the mere immersion of the coating in water pre-press or in
fountain solution or ink on-press, does not produce a suspension or
solution of coating material in the water, fountain, or ink. Only
after the application of mechanical force (with or without the
presence of water or ink) do particles of unimaged coating release
from the substrate.
[0075] If development is undertaken in a two step embodiment,
whereby approximately 95% or more of the unimaged coating is
removed by high pressure water spray or water deposition with
rotating brushes upstream of the press and the residual unimaged
coating is removed by the tack of the ink on press, the particles
are initially removed as a result of active disturbance. Relatively
large particles are dislodged from the substrate, and are carried
away from the plate surface by the flow of water. However, the
particles do not distribute or mix in the water flow, but rather
are merely swept away such that any water with entrained particles
drawn from such flow into a vessel will separate as by settling at
the bottom of the vessel or floating. The residual unimaged coating
removed on-press by the ink and blanket in the second step remains
adhered to the surface of the ink during removal from the substrate
and transfer to the blanket and sacrificial leader paper, without
any dispersion.
[0076] To the extent the particles entrained in the flow are to be
filtered for reuse of the water, it is preferred that such flow be
agitated (as by pumping) to thereby temporarily distribute the
particles so that they can be more uniformly filtered across the
full cross section of the filtering means.
[0077] Thus, the mechanical forces imparted by or during contact
with a fluid such as water, fountain solution or ink, disrupt and
remove only the unimaged areas of the coating from the substrate
surface in the form of undissolved particulate material, without
dispersing the unimaged areas of the coating into the fluid at the
substrate surface as a mechanism of removal from the substrate. The
fluid can be the agent by which the coating material removed from
the surface of the substrate is transferred from the plate to
another operation, such as a filter in the first step or the
blanket of the second step.
[0078] With the pre-press developing embodiment, the rotating
brushes remove the coating whereas the water is merely a flushing
agent to carry away the removed solid particles. Water alone
(without high pressure spray) cannot remove the unimaged coating.
The coating could be removed by the brushes alone but for
convenience the brushes are in the water environment for the
desired flushing action. With pre-press development, the brushes
are relatively coarse and that is why some non-imaged material
remains on the plate, which material is later removed on press via
the tack of the ink. This does not imply that the tack of the ink
must apply a greater force than the brushes.
[0079] On-press development occurs via the ink having been applied
to the plate such that the tack of the ink in contact with the
blanket pulls the unimaged material off the plate. There cannot be
simple water or fountain development on press without the ink roll
on the plate. It should be understood that the term "ink" is used
herein according to the conventional meaning when discussing
lithographic printing, whereby the ink is typically an emulsion of
water entrained in a continuous ink phase. Reference herein to the
"tack" or "adhesion" of the ink encompasses pure ink and such ink
emulsion.
[0080] In a facility where the development is on press, a pre-press
water/brush station or localized steam discharge may desirably be
adapted to process only an edge or corners of the plate with
mechanical force in a water environment where reference numbers or
markers were imaged. The pre-press step will reveal the markers to
the press operator for confirmation that the correct plate is to be
mounted and properly aligned in the press. Preferably the entire
plate includes a top coat of a water soluble oxygen barrier as well
as at least one imaged region of the coating defining a latent
reference mark at a margin of the plate. After imaging of the
plate, the topcoat is washed off with water and the unimaged areas
of only the margin are preferably simultaneously removed with high
pressure water or water with rotating brushes to reveal the
reference mark before subjecting the remaining coating to
mechanical development forces on press.
Coating Chemistry Including Enhancement for Water Penetration
[0081] The following tables contain descriptions of the coating
constituents and variations in the percentage content, associated
with multiple examples of predecessor coatings in which the coating
contained a non-photosensitive, solvent soluble, organic compound
that is partially soluble in water. The imaged plates were
developed by immersion in water and then wiped with a cloth.
Although these tests were not performed in a system as depicted in
FIGS. 1 and 5 with only mechanical force as the developing agent,
the effects of varying the ingredients in a laboratory are believed
applicable for optimizing performance in a production setting where
mechanical force is provided by a high pressure spray. It should be
appreciated, however, that with development according to the
invention in a water spray processor or on press, there would be
much less tendency of redeposition of removed coating material as
reported for some tests.
[0082] In each instance, the plates were prepared in a conventional
manner in a laboratory, with conventional coating weight of 100
mg/sq.ft., drawn down with a wire wound stainless steel rod, and
dried for two minuets at 90.degree. C. All plates had a topcoat of
PVOH at 140 mg/sq.ft. All plates having triazine were imageable
with UV, and all plates with a dye sensitive to 830 nm light
source, such as the KF-1151, were imageable with IR. The results
reported with each table are based on conventional IR imaging at
about 90-100 mj/sq.cm. A dash in a column indicates that the wt %
value is the same as the entry in the previous column of the same
row.
[0083] If the plates are to be processed in a dedicated station
upstream of the press by immersion in water and a wiping action
milder than what a plate experiences on-press, the coating could be
augmented by a release agent, as shown in Table 1.
[0084] Table 2 shows that for a given polymer (Clar. Poly 123) and
monomer (Sartomer 399) combination, the relative weight percent is
a significant variable. Ratios of monomer to polymer in the range
of at least about 1:1 to about 5:1, preferably about 2:1 to about
4:1 are likely to work well, given that the ratio of 0.5:1 (Plate
#4) produced only fair results, the ratio of 4:1 (Plate #3)
produced excellent results, and the ratio of about 9:1 (Plate #2)
produced only fair results.
[0085] Table 3 shows the result that satisfactory plates can be
made from polymer resins that do not necessarily have a reaction to
radiation exposure. The coatings of Plates #1 and #3 have reactive
resins that produced good results, and the coatings of Plates #4
and #5 have non-reactive resins that produced good to fair results.
The potential for use of non-reactive resins opens the door for use
of resins having a much higher molecular weight than presently used
resins.
[0086] Table 4 demonstrates that not all monomers at a given weight
percent of the coating, produce equivalent results, with some
producing poor results. Similarly, Table 5 demonstrates that
potential stabilizers other than DTTDA that are soluble in the
non-aqueous solution and are partially soluble in water, do not
necessarily produce satisfactory results.
[0087] Table 6 demonstrates that potential release agents other
than 4-HBSA that are fully soluble in both non-aqueous solutions
and water can be successfully utilized.
[0088] Table 7 demonstrates that a coating that is sensitive to
both UV and IR radiation can be successfully imaged and processed
in water according to the invention.
[0089] Table 8 demonstrates that good results do not depend on use
of only one kind of initiator.
[0090] Table 9 shows that the use of coinitiator compounds and/or
post-imaging heating, can improve the performance of the
plates.
[0091] In Table 9 the organo-borate compound is P3B, made by Showa
Denko K.K., headquartered in Tokyo, Japan. The P3B can be used as
the sole initiator. It is believed that used individually, the
listed initiators would rank from strongest to weakest as Diphenyl
Iodonium hexaflouro phosphate, Triazine AC, and P3B. The reason for
using a coinitiator system rather then increasing a single
initiator is that there is a synergistic effect between the
organo-borate and either the triazine or onium catalyst. Given a
fixed amount of energy the initiators individually (at their
optimum level) will only produce a certain amount of free radicals.
However, when the organo-borate is combined with one of the other
catalysts, free radicals are generated at a faster rate by the
triazine or onium catalyst while free radicals are still generated
(at a normal rate) from the organo-borate. Therefore the efficiency
of the system is increased in both rate and population. By using
this combination, a much higher degree of cross-linking is
realized, which improves both adhesion and cohesion of the image.
With an increase in adhesion and cohesion, an increased amount of
release agent can be used, thereby providing for better
development.
[0092] Depending on the type of equipment used for the post-imaging
thermal enhancement, a different range of times and temperatures
should be used. With a convection oven, both the temperature and
dwell time are greater than with a small preheat oven unit (where
the plate comes in direct contact with the heating element). As a
rough guide, 200 deg. F. at 1 minute in a convection oven has
approximately the same effect as 175 deg. F. for 7 seconds in a
preheat oven. With a typical commercially available preheat unit,
the window would be 175 to 250 deg. F. for a time period of 5 to 15
seconds.
[0093] Tests were also run on the six formulations shown in Table
9, for comparison of UV versus IR exposures. Previous formulations
which did not contain the organo-borate co-initiator system were UV
sensitive only when they contained the Triazine AC. The onium salt
by itself was not UV sensitive. Incorporating the organo-borate
into the formulation rendered the formulations that contained the
onium salt UV sensitive. All six of the formulations that contained
the co-initiator system produced a good image when exposed to
either IR or UV. In order to simplify the testing formulation #5
was chosen for testing in UV exposures.
[0094] Using an Ugra scale for comparison, plates were exposed for
250, 125 and 62.5 mjs. The plates were then developed through a
water bath with two molleton socks at 4 feet per minute at 75
degrees F. The resulting step wedges were 250 mj--solid 9 steps
with 2 gray steps to a total of 11, 125 mj--solid 7 steps with 2
gray steps to a total of 9 and 62.5 mj--solid 5 steps with 2 gray
steps to a total of 7. All of the images from the different
exposures exhibited very good solvent resistance. The best
resolution that was received was at 62.5 mjs, which yielded an open
15 micron line target and good screen values from 2% to 99%.
TABLE-US-00001 TABLE 1 Coating Compositions With Partially Water
Soluble Stabilizer As The Significant Variable 4-Hydroxy B S A and
DTTDA #1 #2 #3 #4 #5 #6 Meth. Prop.sup..(a) 92.39% 91.99% 92.27%
91.77% 91.77% 91.77% Sartomer 399.sup.(b) 2.31% 2.31% 2.31% 2.31%
2.31% 2.31% Clariant Poly 0.46% 0.46% 0.46% 0.46% 0.46% 0.46%
123.sup.(c) Triazine AC.sup.(d) 0.45% 0.45% 0.45% 0.45% 0.45% 0.45%
DTTDA.sup.(e) 0.00% 0.40% 0.00% 0.40% 0.52% 0.00% 4-HBSA.sup.(f)
0.00% 0.00% 0.12% 0.12% 0.00% 0.52% KF-1151.sup.(g) 0.05% 0.05%
0.05% 0.05% 0.05% 0.05% Pigment 4.34% 4.34% 4.34% 4.34% 4.34% 4.34%
Disp.sup..(h) 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%
.sup.(a)Solvent (1-Methoxy-2-Propanol, Propylene Glycol Methyl
Ether available from Arco Chemical Company) .sup.(b)Monomer
(Dipentaerythritol Monohydroxypentaacrylate available from Sartomer
Company, West Chester, Penn.) .sup.(c)Polymer .sup.(d)Initiator
.sup.(e)Stabilizer .sup.(f)Release Agent .sup.(g)Dye
.sup.(h)Pigment Results: #1) Plate would not develop #2) Plate
showed slight signs of development #3) Plate had partial
development with heavy redeposition #4) Plate developed very easily
producing an image with good adhesion, good dot reproduction and a
clean background. #5) Plate did not develop any better than plate
#2 #6) Plate developed in a very non uniform way yielding a weak
image and redeposition
TABLE-US-00002 TABLE 2 Coating Compositions With Monomer/Polymer
Ratio As The Significant Variable Monomer/Polymer Ratio #1 #2 #3 #4
#5 #6 Meth. Prop. 92.39% -- -- -- -- -- Sartomer 2.77% 2.49% 2.21%
1.85% 0.92% 0.00% 399 Clar. Poly 0.00% 0.28% 0.56% 0.92% 1.85%
2.77% 123 Triazine AC 0.45% -- -- -- -- -- DTTDA 0.40% -- -- -- --
-- 4-HBSA 0.12% -- -- -- -- -- KF-1151 0.05% -- -- -- -- -- Pigment
4.34% -- -- -- -- -- Disp. 100.0 100.0 100.0 100.0 100.0 100.0
Results: #1) Plate produced a good image but the plate was easily
over developed. The coating was slow in speed and had poor adhesion
to the substrate. #2) Produced a better image than #1 with faster
speed but it was still easy to over develop but with better
adhesion. #3) Produced a strong image with good adhesion. The
coating developed very easily with good dot reproduction and clean
background. #4) Produced a very strong image with great adhesion.
The coating was more difficult than #3 to develop but had good dot
reproduction and a clean background. There was also some evidence
of redeposition. #5) Plate showed only very slight development. #6)
Plate had no development.
TABLE-US-00003 TABLE 3 Coating Compositions With Radiation
Sensitive Resin As The Significant Variable Reactive and Non
Reactive Resins #1 #2 #3 #4 #5 #6 Meth. Prop. 92.39% -- -- -- -- --
Sartomer 2.21% -- -- -- -- -- 399 Triazine AC 0.45% -- -- -- -- --
DTTDA 0.40% -- -- -- -- -- 4-HBSA 0.12% -- -- -- -- -- KF-1151
0.05% -- -- -- -- -- Pigment 4.34% -- -- -- -- -- Disp. Clar. Poly
0.56% -- -- -- -- -- 123 Jaylink 106 -- 0.56% -- -- -- -- NK-P1002
-- -- 0.56% -- -- -- Dow -- -- -- 0.56% -- -- Corning 62230
Sartomer -- -- -- -- 0.56% -- PRO5542 4-vinyl- -- -- -- -- -- 0.56%
phenol/ MMac. 100.0 100.0 100.0 100.0 100.0 100.0 Results: #1)
Produced an image with good dot reproduction and adhesion along
with a clean background. Coating was easy to develop. #2) Coating
was difficult to develop and produced a broken image with poor
adhesion. The background of the plate was clean. #3) The coating
was slightly more difficult to develop then #1 but produced an
image with good adhesion but significant coating re-deposited on
the image. The background area of the plate was clean. #4) This
resin (non photo reactive) produced a coating that was easy to
develop. The image had good dot reproduction and good adhesion. The
image was prone to over development. The background areas of the
plate were clean. #5) This resin (non photo reactive) produced a
coating that was easy to develop without being over sensitive. The
image had good dot reproduction and good adhesion. The background
areas of the plate were clean. #6) This resin (non photo reactive)
produced a coating that was very difficult to develop. Could not
get good dot reproduction or a clean background.
TABLE-US-00004 TABLE 4 Coating Compositions With Monomer Type As
The Significant Variable Monomers #1 #2 #3 #4 #5 #6 Meth. Prop.
92.39% -- -- -- -- -- Clar. Poly 0.28% -- -- -- -- -- 123 Triazine
AC 0.45% -- -- -- -- -- DTTDA 0.40% -- -- -- -- -- 4-HBSA 0.12% --
-- -- -- -- KF-1151 0.05% -- -- -- -- -- Pigment 4.34% -- -- -- --
-- Disp. SR-399 2.49% -- -- -- -- -- SR-454 -- 2.49% -- -- -- --
SR-350 -- -- 2.49% -- -- -- SR-295 -- -- -- 2.49% -- -- CD-580 --
-- -- -- 2.49% -- SR-348 -- -- -- -- -- 2.49% 100.0 100.0 100.0
100.0 100.0 100.0 Results: #1) (SR-399 Dipentaerythritol
Pentaacrylate) This monomer produced a coating that was easy to
develop. The image was strong with good dot reproduction and good
adhesion. The background area was very clean. The image was
slightly sensitive to overdevelopment. #2) (SR-454 Ethoxylated
Trimethylolpropane Triacrylate) This monomer produced a coating
that was very easy to develop but had a weak image and a dirty
background. #3) (SR-350 Trimethylolpropane Triacrylate) This
monomer produced a coating that was somewhat difficult to develop.
The resulting image was strong but with heavy retention in
Background. #4) (SR-295 Pentaerythritol Triacrylate and
Tetraacrylate) This Mixture of monomers produced a coating that was
almost as As easy as #1 to develop. The image was slightly weaker
then#1 but the background was clean. #5) (CD-580 Alkoxylated
Cyclohexane Dimethanol Diacrylate) This monomer produced a coating
that did not develop. #6) (SR-348 Ethoxylated Bisphenol A
Dimethacrylate) This monomer produced a coating that was very
difficult to get any development.
TABLE-US-00005 TABLE 5 Coating Compositions With DTTDA And Other
Partially Soluble Stabilizers As The Significant Variable DTTDA and
Analogous Compounds #1 #2 #3 #4 #5 #6 Meth. Prop. 92.39 -- -- -- --
-- Sartomer 399 2.31 -- -- -- -- -- Clar. Poly 123 0.46 -- -- -- --
-- Triazine AC 0.45 -- -- -- -- -- 4-HBSA 0.12 -- -- -- -- --
KF-1151 0.05 -- -- -- -- -- Pigment Disp. 4.34 -- -- -- -- -- DTTDA
0.40 -- -- -- -- -- Dimethyl -- 0.40 -- -- -- -- Tartrate Di allyl
-- -- 0.40 -- -- -- Maleate Di allyl -- -- -- 0.40 -- -- Succinate
Dimethyl -- -- -- -- 0.40 -- Maleate Tetra Methyl -- -- -- -- --
0.40 Tartaramide 100.0 100.0 100.0 100.0 100.0 100.0 Results: #1)
Good development, good image and clean background. #2) Hard to
develop, strong image and dirty background. #3) Very slight
development. #4) No development #5) No development #6) As good as
#1
TABLE-US-00006 TABLE 6 Coating Compositions With 4HBSA and Other
Soluble Release Agents As The Significant Variable 4-Hydroxy B.S.A.
and Analogous compounds #1 #2 #3 #4 Meth. Prop. 92.39 -- -- --
Sartomer 399 2.31 -- -- -- Clar. Poly 123 0.46 -- -- -- Triazine AC
0.45 -- -- -- DTTDA 0.40 -- -- -- KF-1151 0.05 -- -- -- Pigment
Disp. 4.34 -- -- -- 4-HBSA 0.12 -- -- -- Benzene Sul. Acid -- 0.12
-- -- 4-Hydroxy Benzoic Acid -- -- 0.12 -- Sodium Benzoate -- -- --
0.12 100.0 100.0 100.0 100.0 Results: #1 Control formula - produced
a coating that was easy to develop. The image was strong and the
background was clean. #2 The coating was not as easy to develop but
the image was strong and the background was somewhat clean. #3 This
material produced a coating that was as good or better than the
control. #4 This coating was equivalent to #2.
TABLE-US-00007 TABLE 7 Coating Compositions With Various Infrared
Sensitive Dyes As The Significant Variable Various 830 Dyes #1 #2
#3 #4 Meth. Prop. 92.39 -- -- -- Sartomer 399 2.31 -- -- -- Clar.
Poly 123 0.46 -- -- -- Triazine AC 0.45 -- -- -- DTTDA 0.40 -- --
-- 4-HBSA 0.12 -- -- -- Pigment Disp. 4.34 -- -- -- KF-1151 0.05 --
-- -- ADS-WS -- 0.05 -- -- Few Chem S0456 -- -- 0.05 -- Few Chem
S0306 -- -- -- 0.05 100.0 100.0 100.0 100.0 Results: #1 This is the
control coating which developed easily and produced a good image
and clean background. #2 This coating was equivalent to #1 except
that the image was not quite as strong. #3 This coating developed
easily but did not produce any image. #4 This coating developed
easily but produced a very weak image. Observation; Although not
all of the coatings produced an image in the IR all of them did
produce strong images in the UV.
TABLE-US-00008 TABLE 8 Coating Compositions With Triazine Vs. Onium
Salts As The Significant Variable For Cross Linking Initiators
Initiators: Triazine Vs. Onium Salts #1 #2 #3 Meth. Prop. 92.39 --
-- Sartomer 399 2.31 -- -- Clar. Poly 123 0.46 -- -- DTTDA 0.40 --
-- 4-HBSA 0.12 -- -- KF-1151 0.05 -- -- Pigment Disp. 4.34 -- --
Triazine AC 0.45 -- -- Diphenyl Iod. PF6 -- 0.45 -- CD1012 -- --
0.45 100.0 100.0 100.0 Results: #1 This is the control formulation
which was easy to develop and produced a strong image with a clean
background. #2 This formula (with Diphenyliodonium
Hexafluorophosphate) developed easier then the control and still
produced a strong image with a clean background. #3 This
formulation was slightly more difficult to develop than the
control. It produced a strong image but a slightly dirty
background. (Diaryliodonium Hexaflouroantimonate)
TABLE-US-00009 TABLE 9 Post-Imaging Thermal Enhancement and Coating
Compositions with Co-Initiators #1 #2 #3 #4 #5 #6 Meth. Prop.
91.87% 91.77% 91.25% 91.87% 91.77% 91.25% Sartomer 399 2.46% 2.46%
2.46% 2.46% 2.46% 2.46% Clar. Poly 123 0.31% 0.31% 0.31% 0.31%
0.31% 0.31% DTTDA 0.40% 0.40% 0.80% 0.40% 0.40% 0.80% 4-HBSA 0.12%
0.12% 0.24% 0.12% 0.12% 0.24% KF-1151 0.05% 0.05% 0.05% 0.05% 0.05%
0.05% Pigment Disp. 4.34% 4.34% 4.34% 4.34% 4.34% 4.34% Showa D.
3PB -- 0.10% 0.10% -- 0.10% 0.10% Triazine AC 0.45% 0.45% 0.45% --
-- -- Diphnly -- -- -- 0.45% 0.45% 0.45% Iod.PF6 Total 100.0 100.0
100.0 100.0 100.0 100.0 Results: #1a) This is a control type
coating formula which developed easily and produced a good image
and clean background. The run length of this image was very
susceptible to press type and conditions. #1b) Using the same
coating formula the plate was put through a pre-heat of 100 degrees
C. for 1 minute prior to being mounted on press. The plate still
had good development (slightly less then #1a) but had an image that
was less susceptible to the type of press and its condition. #2a)
This is the control formulation but with the addition of a small
amount of an organo-borate compound (Showa D. 3PB) used as a
co-initiator. This plate took longer to develop than plates 1a or
1b but had a much more durable image. This coating was much less
sensitive to press type or conditions and also had better run
length than 1b. #2b) Using the same coating formula as 2a the plate
was put through a pre-heat of 100 degrees C. for 1 minute prior to
being mounted on press. The plate was slower to develop than 2a and
although the image was much tougher the background was not as clean
causing the plate to print with a background tone. #3a) This
coating was the same as #2 but the amount of DTTDA and 4-HBSA was
doubled, which with the use of the organo-borate allowed the plate
to have good development characteristics along with a good image.
This made it easier to develop then 2a but it did not have as tough
an image. #3b) This is coating 3a but the plate was exposed to a
pre-heat of 100 degrees C. (for 1 minute) prior to being mounted on
the press. This plate had a very tough image but was slower to
develop then 3a and did not have a completely clean background.
#4a) This is the same as formula #1 but the Triazine AC was
replaced with the onium salt Diphenyl Iodonium Hexa-Flouro
Phosphate. This change not only allowed the plate to develop faster
on press but it also produced a slightly better image then #1 with
a good clean background. #4b) This is coating 4a except the plate
was exposed to a pre-heat of 100 degrees C. for 1 minute prior to
mounting on press. The plate developed as fast as #1 having a
strong image with good integrity. The plate had a decent run but
was still somewhat susceptible to press conditions. #5a) This is
the same as coating 4a except for the organo-borate. The plate
produced from this coating was slower to develop than plate 4a. It
had a good image with a clean background. #5b) This is coating 5a
with a preheat of 100 degrees C. for 1 minute prior to mounting on
press. This coating developed at approximately the same speed as
5a. The image was very strong with good integrity but the
background printed with a very slight tone. #6a) This is coating
formula #5 with double the amount of the DTTDA and 4-HBSA. These
plates had a good roll up on press with a clean background. The
image was sound but not quite as strong as #5. #6b) These plates
were coated with the formula of #6 but were exposed to a pre-heat
prior to being mounted on press. In the previous pre-heat trials
the plates could not exceed a temperature of 100 degrees C. without
either losing a clean background or loss of development altogether.
With the increase in the developing aids the plates were able to
take a pre-heat of 120 degrees C. for 1 minute and still maintain
good development with a strong image and a clean background.
Coating Chemistry Without Enhancement for Water Penetration
[0095] Although the Tables above were based on varying the
components of a composition which included a solvent soluble,
partially water soluble organic compound, the effects of these
variations are likely to be instructive for compositions without
such organic compound. It should be appreciated that a key aspect
of the embodiment without the partially water soluble organic
compound, is that the cohesion of the unimaged coating is greater
than the adhesion of the unimaged coating to the substrate. Some
compositions in the foregoing tables that show promise (because of
the efficacy of the partially soluble compound) may not be suitable
for this embodiment if the adhesion is not less than the cohesion,
however, one of ordinary skill in the art can readily select and
optimize many of the compositions in the Tables by omitting the
partially water soluble organic compound.
[0096] There are many types of resins, oligomers and monomers that
can be used to produce coatings that would have properties suitable
for use in the present invention. It is believed that the monomer
to polymer ratio in the range of 2-4 and the use of an
organo-borate catalyst with an onium salt catalyst are important
preferences. A wide mixture of functionalities can be used but
dried coatings with better adhesion and cohesion are achieved with
multi functional monomers and oligomers (functionality of 3 or
higher). It is not necessary to use a resin which contains
unsaturated groups but in the majority of the cases the cured film
will exhibit better adhesion and integrity. Types of resins can
include poly vinyls (poly vinyl acetate, poly vinyl butyral, etc),
cellulosic, epoxies, acrylics and others as long as the resin does
not produce a strong adhesive bond with the substrate. Monomers and
oligomers should be somewhat viscous liquids and can be
polyester/polyether, epoxy, urethane acrylates or methacrylates
(such as polyether acrylate, polyester acrylate, modified epoxy
acrylate, aliphatic urethane methacrylate, aliphatic urethane
acrylate oligomers, polyester acrylate oligomers, aromatic urethane
acrylate, dipentaerythritol pentaacrylate, pentaacrylate ester,
etc.).
Clean Fountain Water and Press Ink
[0097] Upon further investigation of on-press development using the
tension forces imposed on the ink between the imaged coating and
the blanket roll to pull off the nonimage areas as particulates
without dissolution, we have discovered that neither the fountain
water nor press ink is contaminated with resinous material or
colorant. This overcomes the problems faced by the known on-press
methods, as discussed in the Background portion of the present
specification.
[0098] As used herein, "fountain water" includes substantially pure
water as well as fountain solution, which is predominantly water
with other materials in solution such as alcohol. These materials
are colorless and do not contribute to the problems caused by
dissolution of water-soluble resin and other active ingredients in
the oleophilic coating. Similarly, a typical water soluble oxygen
barrier such as PVOH has no more adverse effect than the alcohol in
fountain solution. As used herein, "press ink" should be understood
as an emulsion of fountain water droplets distributed in an ink
continuum applied as a film on the plate cylinder in a wet press.
The fountain water volume content is typically about 4%. Also, the
terms "unimaged coating areas" and "nonimage coating areas" are
synonymous.
[0099] One particular method of imaging and on-press development of
a lithographic printing plate according to this advantage of
removing undissolved particles of non image coating, begins with
selecting a plate having a substrate with (i) a grained and
anodized hydrophilic surface, (ii) a negative working, organic,
polymerizable coating of at least one layer, which coating includes
(a) active components for polymerization which are all insoluble in
any of the group of fluids consisting of water, fountain solution
and ink, (b) an optional water insoluble colorant, and (c) an
optional non-active, non-resinous, non-colorant water soluble
material, e.g., DTTDA. The coating is non-ionically bonded to the
substrate. The non-active, non-resinous, non-colorant water soluble
material can be one or both of an oxygen barrier, or an ingredient
in the oleophilic coating, such as a partially water soluble,
organic compound, e.g., DTTDA. In these coating compositions, the
effective solubility in water is very low, e.g., such organic
compound constitutes less than one weight percent of the coating
weight and exhibits only a partial solubility in water of less than
about 15 percent. As described elsewhere herein, the partially
water soluble compound is not required because purely mechanical
forces are sufficient to remove the non image coating areas.
Preferably, none of any components of the PS coating is soluble or
dispersible in press ink or fountain water.
[0100] The plate is imaged with radiation, especially by heating
with infrared radiation, to activate the active components and
thereby produce a pattern of relatively hardened image areas and
as-coated nonimage areas that that were not affected by the
radiation. As a consequence, the cohesion of the image areas is
greater than the cohesion of the non image areas and the adhesion
of the image areas to the substrate is greater than the adhesion of
the nonimage areas to the substrate.
[0101] For on-press development, any topcoat oxygen barrier can be
washed off before the plate is mounted to the plate cylinder of the
press, or removed by the water present in the fountain fluid. On
press, the ink form roll contacts and applies an ink film on the
entire oleophilic coating. The ink film adheres to the oleophilic
coating due to the adhesion of the ink continuum. Then the blanket
roll contacts the coating while the plate is rotated on the plate
cylinder. It should be appreciated that the ink film can be applied
to the plate from a source of the emulsion, or by merging distinct
sources of ink and fountain fluid, as is well known in the art. A
rubber roll is opposed to the blanket roll.
[0102] When a newly mounted plate is on the press, a paper leader
from a paper roll is fed between the blanket and rubber rolls, and
these rolls are rotated to advance paper there between until the
plate is fully developed, i.e., until the paper output no longer
carries transferred particles of nonimage coating, at which point
normal production printing begins.
[0103] Development occurs during multiple revolutions of the rolls
whereby with each revolution increasing areas of the plate
substrate are revealed as successive particles of nonimage coating
are randomly and mechanically removed from the substrate. The
blanket roll applies sufficient tension to the ink whereby the tack
of the ink pulls off only nonimage areas from the substrate in the
form of undissolved coating particles, including all the
polymerization initiator, dye compound, and colorant that are
transferred by the blanket with the ink to the paper leader. The
preferred relationships of adhesion and cohesion on-press are shown
in FIGS. 8-11.
[0104] During this process the ink emulsion splits whereby some of
the initially entrained water adheres to the increasing surface
areas of revealed, hydrophilic substrate. The remaining ink still
contains some water as an emulsion. Importantly, none of the water
on the substrate or in the ink contains any oleophilic material,
dyes, colorants, resins, initiators or the like in dissolved form,
because these were removed from the plate as undissolved solids and
are ultimately transferred to the paper leader. The water on the
substrate and the ink emulsion adhered to the image areas are
transferred by the blanket to the paper without contamination by
dissolved coating material.
[0105] It should be understood that the nonimage particles removed
in accordance with the invention are large relative to the
thicknesses of the PS coating and the ink pulled by the blanket.
The PS coating thickness is typically in the range of 2-3 microns
and the ink film thickness is typically less than 2 microns. The
particles dislodged from the substrate retain the original PS
coating thickness but would have a surface area ranging from the
smallest screen size (in regions for printing shadows) to several
square inches or more (in regions where the print image has white
background). In an imaged plate for printing at a relatively high
2400 dpi resolution, the equivalent pixel area is 30-40 micron,
which is at least ten times the thickness of the ink.
[0106] Since the resinous coating is not soluble or dispersible
when contacted with fountain or ink, no development occurs before
or during engagement of the plate by the ink form roll. It should
be understood that in the present context this means the resinous
coating does not dissolve or disperse in pure ink, press ink, pure
water, or fountain solution. The nonimage coating areas are removed
only when the blanket engages the inked plate, whereby the nonimage
areas are pulled off from the substrate. When considered at a
microscopic level, the particles are in essence delaminated from
the substrate in the form of large, thin flat platelets adhered to
the tacky surface of a comparably thin film of the ink emulsion.
These relatively large platelets do not dissolve in and cannot
disperse into the ink emulsion. Not only are the platelets far too
large relative to the ink film to disperse in (become distributed
throughout) the ink film, but once the coating dislodges from the
substrate as platelets there is no compression between the ink and
the coating that would force platelets into the ink film. It should
be understood that the invention does not require that a large
expanse of nonimage coating (e.g., several square inches)
necessarily be dislodged as a single platelet during one revolution
of the blanket. As discussed above, even the smallest platelet
dislodged or broken off from a large expanse or only one pixel, is
large as compared to the thickness of the ink film.
[0107] The difference in development mechanisms between reliance on
mechanical forces and reliance on water sensitivity can be inferred
from a comparison of wetting out characteristics derived from Table
10.
TABLE-US-00010 TABLE 10 Radiation Curable Coatings With and Without
Water Soluble Components Formulations Ingredients #1 #2 #3 #4 #5 #6
#7 PGME 94.990 94.990 94.990 94.990 94.990 94.990 94.990 Poly 123
1.500 -- -- 1.500 1.389 1.364 1.272 Bayhydrol 2280 -- 1.500 -- --
-- -- -- ACA Z250 -- -- 1.500 -- -- -- -- Sartomer 399 1.750 1.500
2.000 1.500 1.852 1.818 1.271 Satomer 454 0.250 0.250 -- -- -- --
-- Sartomer 355 -- 0.250 -- -- -- -- -- Sartomer 9035 -- -- --
0.500 -- -- 0.423 IRT thermal Dye 0.150 0.150 0.150 0.150 0.139
0.136 0.127 Penn Color 0.350 0.350 0.350 0.350 0.324 0.318 0.297
Na-TP Borate -- -- -- 0.200 0.084 -- 0.339 HOINPO2 0.400 0.350
0.050 -- 0.286 0.364 -- Showa-Denko P3B -- 0.050 0.350 0.200 -- --
-- Phenothiazine 0.010 0.010 0.010 0.010 0.010 0.010 0.010
Showa-Denko 2074 0.600 0.600 0.600 0.600 0.556 0.546 0.509
4-HBSA/Na -- -- -- -- 0.370 -- 0.339 Simusol NW342 -- -- -- -- --
0.454 0.423 TOTAL 100.00 100.00 100.00 100.00 100.00 100.00
100.00
[0108] Formulations #1, #2 and #3 are examples of radiation curable
coatings that contain no water soluble or water dispersible
ingredients. Formulations #4, #5, #6 and #7 are examples of
radiation curable coatings that use water soluble or water miscible
ingredients. Formulation #4 contains a water soluble monomer
(Sartomer 9035) and a water soluble catalyst (Na-TP borate).
Formulation #5 contains a water soluble catalyst (Na-TP Borate) and
a water soluble stabilizer (4-HBSA/Na). Formulation #6 contains a
water soluble/miscible non-ionic surfactant (Simusol NW342).
Formulation #7 contains all of the water soluble/miscible
ingredients that are used in formulations #4, 5 and 6.
[0109] Imaged coatings with any of these seven formulations can be
developed with high pressure water spray, water and rotating brush,
or directly on press. The main difference is that formulations #1,
2 and 3 contain no ingredients that are water soluble or miscible,
whereas formulations #4-7 contain at least one ingredient that is
water soluble or miscible. Formulations #1-3 are consistent with
the present invention, to the effect that a wide range of
ingredients can be used in order to produce a lithographic printing
that can be developed using only a mechanical force applied to the
coating, without reliance on dissolution or dispersion of the
coating in water (e.g., fountain fluid) or press ink.
[0110] The coatings that are produced from formulations #4-7 rely
for development, on their solubility/miscibility in water and/or
press ink. Press ink carries approximately 4% water, and known
aqueous developable plates or plates that are developable on press
in ink and/or fountain fluid incorporate some form of water
sensitive ingredient (e.g., soluble/miscible material) in order to
initiate and complete the development process. The water sensitive
ingredients can be polymers, oligomers, monomers, catalysts,
stabilizers and a number of other materials that are used to help
coat ability, developability, hydrophilicity of the non image area,
shelf life of the plate, pot life of the coating solution, etc. The
water that is contained in the aqueous developers, fountain
solutions and press inks either completely dissolves the non imaged
areas of the coating or produces a more limited dissolution which
allows the water to percolate through the film. Whether complete or
limited, the dissolution of the film is controlled by the type and
the amount of water sensitive ingredients that are used. Once the
water is able to reach the hydrophilic surface of the substrate it
undermines the non imaged area of the coating so that it can be
further dissolved or dispersed in the water and/or ink.
[0111] Formulation #6 contains a surfactant which in practice
produces a functionally similar effect on the water-insoluble
ingredients of the coating, as water produces in dissolving
water-soluble ingredients in coating formulations #4, 5, and 7.
During aqueous development or on press, the surfactant penetrates
the surface of the coating and on a microscopic or molecular level
(analogous to dissolution) disassembles the integrity of the
coating such that the coating disperses into the water or fountain
fluid.
[0112] As previously described, a number of problems are associated
with plates having coatings formulated with water sensitive
materials. The imaged area of the coating that does the printing
becomes less oleophilic which causes it to be less ink receptive.
The imaged area of the plate tends to have poorer adhesion to the
substrate, causing premature wear of the image producing short run
lengths. When developed on press the water sensitive materials in
the coating will cause the rest of the materials in the coating to
be dissolved and/or dispersed in the fountain solution and ink.
This will in turn cause other problems: The colorants (pigments and
dyes) will cause the lighter inks to discolor (for example blue
dyes and pigments will cause the yellow inks to turn green and the
red inks purple). The water sensitive materials will cause the ink
and the fountain solution to emulsify which will cause the plates
to scum which in turn will produce dirty copies.
[0113] All plates having coating formulations #1-3 are comprised of
a substrate with a hydrophilic surface and a very oleophilic
radiation sensitive layer, but the mode of development of coating
formulations #1-3 relies strictly on the adhesive and cohesive
properties of the coating. These coatings as applied and prior to
imaging exposure have better cohesive strength than adhesive
strength. The adhesive strength of the ink to the non imaged
coating is greater then the adhesive strength of the coating to the
substrate. When the coating is exposed to radiation it undergoes
polymerization which greatly amplifies its adhesive and cohesive
strengths. The unexposed coating has weaker adhesion to the
substrate and weaker cohesion to itself than that of the press
inks. The higher surface energy of these coatings allows the press
ink to adhere very strongly. This strong adhesion along with its
greater cohesive strength allows the ink to delaminate the coating
from the plate surface.
[0114] The imageable films produced from the seven coating
variations listed above were tested for their surface energy and
their ability to wet out with water. The extent of wetting is
commensurate with the extent of solubilization or dispersion in
water. The results of these tests can be seen in Table 11.
TABLE-US-00011 TABLE 11 Wetting Characteristics Described By
Contact Angle Formulations #1 #2 #3 #4 #5 #6 #7 Time in 0 69.8 70.1
70.8 67.6 67.7 69.2 68.1 Seconds 1 71.7 72.1 71.8 48.2 66.5 65.6
65.0 2 71.6 71.9 71.6 47.0 66.3 65.2 57.3 3 71.5 71.9 71.6 46.6
66.3 65.0 55.5 4 71.5 71.8 71.5 46.4 66.2 64.8 54.1 5 71.4 71.8
71.5 46.2 66.2 64.6 53.1 6 71.4 71.6 71.4 46.1 66.3 64.5 52.6 7
71.4 71.6 71.3 46.0 66.2 64.4 52.6 8 71.2 71.5 71.3 45.8 66.2 64.2
52.5 9 71.2 71.5 71.2 45.6 66.2 64.2 52.3 10 71.2 71.5 71.2 45.6
66.1 64.2 52.1
[0115] These tests were performed with a "Drop Shape Analysis
System" DSA10 Mk1 that is manufactured by Kruss. The system
measures the contact angle of a drop of water placed on the surface
of the coatings of interest. The angle is formed by the tangent of
the drop to the surface that it sits on. The higher the angle the
more oleophilic the surface. The analysis is performed over a
specified period of time in order to record any changes in the
contact angle. If the contact angle starts high and remains that
way then the surface is considered to be water repellent. The lower
the contact angle and the more that it decreases over time
indicates the water receptivity of the coating. Table 11 shows that
formulations #1, 2 and 3 have contact angles that start high and
remain virtually unchanged. Conversely, the data indicates that
formulations #4, 5, 6 and 7 produce films that are water receptive.
This is seen in that the contact angles start out lower (than #s 1,
2 and 3) and continue to decrease over a 10 second period. The more
of a decrease that occurs the more the water is wetting out the
surface and thus indicates that it is more water receptive.
[0116] After completion of the contact angle test the surfaces of
the various coatings were inspected for any deterioration that
occurred from the water drop. Coatings #1, 2 and 3 had no visible
signs of attack. Coating #5 showed partial dissolution of the
coating whereas coatings #4, 6 and 7 were completely dissolved.
[0117] A rub test was performed on each coating formulation using
"virgin" ink (no water) for one test and press ink for a second
test. All plates had a water-soluble top coat. The results can be
seen in Table 12.
TABLE-US-00012 TABLE 12 Number of Double Rubs Virgin Ink Press Ink
Formulation #1 10 rubs *10 rubs #2 10 rubs *10 rubs #3 10 rubs *10
rubs #4 10 rubs 2 rubs #5 10 rubs.sub.- 3 rubs #6 10 rubs 1 rubs #7
10 rubs 1 rubs
[0118] None of the formulations had any sensitivity to virgin ink.
In plates with formulations #1-7 the virgin ink did not penetrate
the hydrophilic top coat so none of the resinous coating was
removed. The asterisks indicate that some coating was removed. When
press ink was used on plates with formulations #1-3, the water in
the press ink evidently penetrated the topcoat and the relatively
mild compressive and shearing forces of the ten double rubs,
mechanically pulled off a portion of the resinous coating from the
substrate. In plates with formulations #4-7, the topcoat was also
removed by the water in the press ink, but in addition the water in
the ink dissolved and completely removed the resinous coating in no
more than three double rubs. These tests confirm that the
developing mechanism of plates with coatings #1-3 is very different
from the development mechanism of plates with coatings #4-7.
[0119] The following list of representative ingredients will enable
practitioners in this field to formulate coating compositions that
are adapted to a meet targeted performance that balance cost of
ingredients, coating process control, shelf life, range of imaging
radiation wavelength, type or types of mechanical forces to be used
for development, type of fountain and ink on press, and ease of
achieving target resolution. The formulations #1-7 are thermally
(IR) imageable as promoted by the IRT dye as a polymerization
initiator, but can readily be prepared for either thermal or
ultraviolet (UV) imaging by including a UV sensitive initiator such
as Ciba-Geigy UV-10. The formulations #1-3 shown in Table 10 were
selected for a particular comparison test, but for commercial
purposes additional, non-active water insoluble ingredients can be
included such as viscosity agents for facilitating coating of the
plate, shelf life stabilizers, and agents for reducing any tendency
for removed coating particles to build up in, e.g., a water and
rotary brush processor. In variations not shown in Table 10, the
solvent can be Arcosolve PM, DMF, and MEK; non-active stabilizers,
pigments and the like can include Karenz PE1 and 29S1657 as well as
the ACA Z 250. Urethane acrylate resins with active ingredients
similar to formulation #2 and various water-insoluble inactive
ingredients are presently preferred.
[0120] As a consequence, all of the nonimage coating is removed in
solid particle form by the blanket and deposited on the waste
leader. With the present invention, complete development of the
plate without ink or water contamination is achieved with
significantly fewer revolutions of the rolls. This saves the print
operator significant cost associated with supplying ink and paper
that is wasted in the course of developing the plate.
* * * * *